1. Technical Field
The present invention relates to analytical strips, and more particularly, to an analytical strip for quantitative assay of biological fluid.
2. Description of Related Art
The traditional quantitative biochemical assays usually utilize a specific enzyme to react with a specific analyte and then detect the change of the chemical or electrical property of reactants or products of the reaction. It is conventional, for example, to determine the concentration of glucose in an biological fluid by detecting the variation of voltage or electrical current caused by hydrogen peroxide produced in the reaction of the glucose in the biological fluid and the glucose oxidase immobilized on dissolved oxygen electrodes. The concentration of the hydrogen peroxide is then calculated, followed by the determination of the glucose concentration in the biological fluid, for the concentration of the glucose oxidase is known. Because the amount is relative small for hydrogen peroxide to cause the change of the voltage or the electrical current, electrical chemical assays, such as the assay described above, are advantageous for the volume of the biological fluid required is also relative small and the detection is rapid. However, such assay requires specific enzymes to produce peroxide for detection, and thus is only applicable to quantitative analysis of small molecules, such as glucose, cholesterol, urea, creatinine, etc.
Another known approach is to utilize a unique capability possessed by the immunological molecules, for they can recognize as well as bind the biological molecules specifically. For example, the traditional enzyme linked immunosorbent assay (ELISA), which is typically conducted in a 96-well plate, characterizes in that determining concentration of an analyte (i.e., antigen) by the intensity of a detected signal resulted from the reaction between the analyte, the corresponding immunological molecules, the enzymes and the corresponding reagents. However, users usually need to perform a tedious washing step at every stage in the assay to wash away the non-binding and the non-specific binding molecules to prevent the assay from failure or in case that the false-positive results occur.
With the progress technology, nowadays immunological analytical assays are carried out with the analytical strips which have microfluidic channels to simplify, or even omit, the complicated and repeated washing works traditionally required after every reaction stage of the assay. However, it is inconvenience for the known analytical strip needs manually to add reagents or substrates required for reactions into the analytical strip. The reagents or substrates required for the conventional strips tend to degrade at room temperature or under light after long-term storage, which results in the errors of the assay. Accordingly, such reagents need to be stored in a specific condition, such as cooling or light-proof. Consequently, the conventional analytical strips are nevertheless inconvenient in use and storage
In addition, conventional analytical strips with channels or micro-fluidic channels have other problems. While such a channel or micro-fluidic channel is typically bordered by a non-absorbent material, and the viscosity of the fluid sample to be analyzed is usually high for the sample is mainly composed of proteins or carbohydrates, part of the fluid sample tends to adhere to the surface of the channel and will not be reacted. Such scenario, if happens, will not only disadvantageously cause the waste of the fluid sample to be analyzed, but also will adversely affects the accuracy of quantifying assays.
Moreover, the conventional analytical strip may facilitate the flow of the fluid sample by micro-fluidic channels so that the fluid sample will be delivered via the capillary force exerted by the structures of such channels to the reaction area. Another alternative approach to deliver the fluid sample involves applying a driving force, such as by a pressurizing means, at the time the fluid sample is introduced into the channel so that the fluid sample is propelled to the reaction area through the channel. However, either one of the aforementioned approaches tends to cause air bubbles occurring after the fluid sample is introduced into the channel. These bubbles, either large or small, will block the channel and result in inaccurate analyzing results.